This invention relates to containers constructed with vents which allow release of pressure from inside the container and more particularly to a battery box which is self-venting.
Containers have been constructed with vents in order to allow the passage of a liquid or gas out of the container when the liquid or gas reaches a pressure level above that which the container can accommodate. The release of the pressure prevents potential rupture of the container and prevents a cover of the container from being ejected during removal. It also prevents injury to anyone in the vicinity of the container when rupture or ejection of the cover occurs.
Vented containers have a number of uses including holding batteries. An example of a battery which can cause a volatile reaction and result in extremely large pressure in a container is a lithium sulfur dioxide battery. These batteries are in use in both commercial and in military applications.
One type of military battery operated radio uses a lithium BA-5513 battery. The battery is typically housed in an aluminum, die-cast container which has a vent. The container is designed to contain the pressure caused by any volatile reaction, and the vent allows air to escape to relieve the pressure.
There are two major shortcomings to these vented containers. The first is the cross-sectional area of the vents, which is relatively small when compared to the volume and the velocity of the air that is attempting to exit. Therefore, during a battery explosion, the air pressure increases due to what is essentially a "log-jam" at the vent opening. The increase in air pressure then creates excessive stress on the walls of the container. Since the vents are unable to perform their intended function adequately, the increased stress on the walls of the container often results in catastrophic failure.
The second shortcoming is the construction and material of the containers. The containers are typically aluminum die castings which are very brittle. The material ruptures violently rather than yielding in a ductile manner.
Lithium batteries are known to produce explosions of as high as 400 psi in a few milliseconds. The vents on the containers currently being used for the military radios are incapable of releasing such a rapid increase in pressure thereby creating a major safety hazard.
It is therefore an object of the present invention to provide a container which is self-venting.
It is an additional object of the invention to provide a container for a lithium battery which is capable of alleviating internal pressures in the container in a reliable manner.
It is still another object of the invention to provide a venting battery container which is more economical and easier to fabricate.